National MP Matt King's plan to king-hit coward-punchers

National MP Matt King's proposal to hit killer coward-punchers with 20 years in prison has been drawn from the ballot.

There's just one small problem. He'll likely need Winston Peters' support to get it into law - and he beat the long-remembering NZ First leader in the battle for Northland last year.

"That's politics - I think he's moved on," Mr King told The AM Show on Friday morning.

NZ First has called for minimum eight-year sentences for coward-punchers, while Mr King's Bill allows for up to 20 in the case of death, which he says "signals to the judiciary it's a serious offence and take it seriously".

He's not so sure about a minimum sentence though.

"Mandatory sentencing, there's problems with that. However if it goes through to select committee and the submissions from the public and the various interested parties, including the political parties, want a mandatory sentence, I'm open to that idea. It's not in the original Bill, but I'm open to everything."

Coward punches, or king-hits as they're also known, are an epidemic in Australia. A 2012 study found 91 people had been killed in surprise one-hit punches since 2000, the vast majority happening outside bars in the early hours of the morning.

"The victims are in most cases young men - they're innocent, they're usually unprovoked attacks. They're defenceless because they don't see it coming."

Mr King says while the problem probably isn't as bad here, it's hard to tell because statistics aren't kept - they generally fall under the category of manslaughter.

And the sentences are usually a far cry from those handed down for murders. Tyrone Palmer, who killed a man in Invercargill with a single punch in 2016, was sentenced to only 22 months in prison.

In 2014, a former naval rating who killed a trainee teacher with a single punch got 28 months.

And in Australia, a man who coward-punched a teenager who survived but suffered memory loss, didn't even go to jail. Caleb Maraku instead left court a free man in January this year, smiling and taking selfies with reporters he called "fans".

Green Party justice spokeswoman Golriz Ghahraman said there was no need to change the law.

"An illegal assault that causes death is covered by manslaughter already," she told Newshub, saying National was just trying to look tough.

"It's a little bit of that same brand of being 'tough on crime', so to speak, without really doing anything at all."

Mr King says all of National's 56 MPs are in favour of the Bill, but he is yet to speak to the other parties' MPs - including Mr Peters.

Newshub contacted Justice Minister Andrew Little, who says the Bill is "30 years out of date".

"Mindless prescriptive sentences like this are old-fashioned, they're out of date," he says.

"We actually want a sentence that reflects the gravity, not just the particular occurrence, but the person in front of the judge.

"And if the person in front of the judge has a track record of hitting people seriously, but on this occasion has resulted in a death, you want them to get a harsh sentence - and 20 years might not be enough."